For the stepwise advance of casting moulds consisting of closely juxtaposed mould parts presenting pouring cavities at vertical joint faces between successive mould parts, conveyors are known which comprise a driven, endless, flexible belt. Such a belt may form a continuation of a stationary bed, or pouring channel, which provides a stable support and guiding path for the mould during the pouring operation and, through its friction against the underside of the mould, contributes to keeping the mould parts in close juxtaposition. In smaller units in particular, cooling of the mould containing the castings may also take place on the bed, but often it is desirable to achieve a reduction in the total frictional resistance to the advance of the mould, and to this end the terminating section of the guiding path may be a belt conveyor as referred to above. The flexible belt of the conveyor may be a conventional endless rubber or steel belt but may also consist of wire gauze or hinged slats, and it is known to run such a belt around end rollers, of which at least one is driven in such a way as to drive the mould-carrying belt upper part in the forward direction synchronously with the advance of the mould on the stationary bed. This shall prevent opening and re-closing of the mould at the transition between the bed and the belt, and shall also prevent the risk of deformation or crushing of the mould standing on the bed. Consequently, by a suitable control of the belt movement, a desired weighting between successive mould parts is aimed at.
In practice, however, it has proved very difficult to achieve this object, and moreover it has been ascertained that the mould supported on the belt is not kept stably together but has a tendency to open at the joints. Under such conditions the castings may suffer from cooling damages even if they normally have fully or partially solidified during this phase of the advance movement, and if the counterpressure from the belt exceeds a certain value, pressure damages may be inflicted to the mould supported on the bed.
These adverse conditions must be attributed to the fact that any flexible conveyor belt has a certain longitudinal elasticity and is, therefore, slightly extended during the acceleration of the mould, while it retracts correspondingly during the braking phase. Even in the case of a very precise control of the belt movement with respect to start, travel and stop, it will in practice not be possible to compensate for these small elastic deformations, and even if the detrimental effect thereof can be reduced by transferring only part of the force, required for advancing the mould, via the belt, while the remainder of the force is exerted via a pressure on the mould part last added, this does not prevent the tendency of the mould to open at the joints and avoiding, with safety, deformation of the mould part or parts last added.
The primary object of the invention is to provide a particular belt driving mechanism by which the longitudinal elastic deformations of the belt are avoided or at any rate reduced to an entirely unharmful minimum.